Matched rabbit monoclonal antibodies against αv-series integrins reveal a novel αvβ3-LIBS epitope, and permit routine staining of archival paraffin samples of human tumors

The relationship between integrin expression and function in pathologies is often contentious as comparisons between human pathological expression and expression in cell lines is difficult. In addition, the expression of even integrins αvβ6 and αvβ8 in tumor cell lines is not comprehensively documented. Here, we describe rabbit monoclonal antibodies (RabMabs) against the extracellular domains of αv integrins that react with both native integrins and formalin fixed, paraffin embedded (FFPE) human tissues. These RabMabs, against αvβ3 (EM22703), αvβ5 (EM09902), αvβ6 (EM05201), αvβ8 (EM13309), and pan-αv (EM01309), recognize individual integrin chains in Western blots and in flow cytometry. EM22703 detected a ligand-induced binding site (LIBS), reporting an epitope enhanced by the binding of an RGD-peptide to αvβ3. αvβ8 was rarely expressed in human tumor specimens, and weakly expressed in non-small-cell lung carcinoma (NSCLC). However, ovarian carcinoma cell lines expressed αvβ8, as did some melanoma cells, whereas U87MG glioma lacked αvβ8 expression. We observed an unexpected strong expression of αvβ6 in tumor samples of invasive ductal breast adenoma, colorectal carcinoma (CRC), and NSCLC. αvβ3 was strongly expressed in some invasive NSCLC cohorts. Interestingly, PC3 prostate cell and human prostate tumors did not express αvβ3. The RabMabs stained plasma membranes in FFPE-immunohistochemistry (IHC) samples of tumor cell lines from lung, ovary, colon, prostate, squamous cell carcinoma of head and neck (SCCHN), breast, and pancreas carcinomas. The RabMabs are unique tools for probing αv integrin biology, and suggest that especially αvβ6 and αvβ8 biologies still have much to reveal.